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Protein Synthesis Notes
(247 and 249)
Steps of DNA Transcription
Making mRNA from DNA
1. Helicase does NOT unzip DNA at the gene of
interest
2. RNA polymerase unwinds and matches RNA
nucleotide bases to DNA, using one side as a
template.
3. The mRNA strand is created. It now compliments
the original DNA strand (G-C and A-U).
4. Ligase helps the strand of DNA to close and again.
5. mRNA strand moves out of nucleus to ribosomes,
and the DNA zips up.
Key Players in Translation
rRNA = RNA that makes up a ribosome
tRNA = RNA that transfers specific amino acids
mRNA = carries the DNA message;
RNA transcribed from DNA
Codon = 3 nucleotides in a row on a strand of
mRNA that code for an amino acid
Anticodon = 3 nucleotides in tRNA that base
pair with the codon
Amino Acids = monomers of proteins
(20 in humans)
Steps to Translation
Making proteins from mRNA
1. Ribosomes attach to the “start” codon of
mRNA (AUG), signaling the beginning of the
protein chain
2. mRNA codons are matched to corresponding
tRNA anticodons and appropriate amino acids
are strung together.
3. Dehydration synthesis occurs between the
amino acids, and they join, making a protein
chain with peptide bonds in between
4. Ribosomes detach when they come across a
“stop” codon (UAA, UAG, UGA). Protein
synthesis is complete.
Proteins
•
•
Made up of Carbon, Hydrogen, Oxygen
and Nitrogen (and some Sulfur)
Proteins are responsible for many
reactions
Types of Proteins
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Proteins
2. Structural Proteins
– Provides mechanical support to cells and
tissues
3. Transport Proteins
– Transports small ions or molecules
4. Motor Proteins
– Enables structures to move
Proteins
5. Hormones (signaling proteins)
– Carries signals from cell-to-cell
– e.g., insulin
6. Storage
– Stores small molecules or ions
– e.g., iron is stored in the liver in ferritin
7. Other specialized functions
– Defense (immune system antibodies),
– Receptor proteins (in eyes and muscles to
detect stimulus)